Oleguer has sealed his switch from Barcelona to Ajax after completing a medical.
On Saturday, it was announced that the 28-year-old had penned a contract that will keep him at Amsterdam ArenA until 2011, with the option to extend the deal for a further year.
An initial fee of €3million (£2.4million), which could rise by a further €2.25million (£1.8million) if Ajax qualify for the UEFA Champions League within three seasons, has been agreed between the two clubs.
Head coach Marco Van Basten told Ajax's official website: "We are very pleased with his arrival. He is an excellent defender and is very experienced."
Oleguer added: "I will do my utmost to help the team. Hopefully we can have a successful season. Ajax was the best option for me."